A start-up based in Palo Alto, Calif., Disconnect, which helps you track who is tracking you online, this week released its latest tool to help safeguard your browsing history. Its new browser extension works on Chrome and Firefox browsers and is meant to block an invisible network of around 2,000 separate tracking companies.

Disconnect offers tools to help track who is tracking you online.

Most of the tracking is in the service of advertising: If you were browsing a camping goods site over the weekend, for instance, don’t be surprised to see an ad pop up for hiking boots when you log in to a news site the next morning or even, when you open up your Facebook page.

It is a tried-and-true digital advertising strategy called retargeting. Facebook is the latest entrant, and its advertising partners are experimenting with fine-grained ways to nudge you with ads on Facebook based on what you were looking at when you were not on Facebook.

The Disconnect filter, which Brian Kennish, a former Google engineer, started building two years ago, is squarely aimed at controlling that kind of targeted advertising.

“We are stopping that flow of data as you bounce around the Web,” said Mr. Kennish, a company co-founder. “Third-party retargeters are not going to have information about you.”

The new Disconnect filter is part of an emerging crop of privacy tools aimed at tech-savvy consumers who want to protect personal data online. Most of these companies – Abine and Ghostery are others – offer at least a basic version of their product free and charge for more advanced versions. Disconnect is offering its filter on a sliding scale.

These tracker filters are distinct from the long-debated Do Not Track signals that exist on most Web browsers and that are intended to give users a way to control whether their browsing history can be used for targeted advertising. Digital advertisers have fought hard against industrywide standards. And at the moment, even if a consumer turns on the Do Not Track signal on her browser, advertisers are not obliged to honor it.

The filters, like the one from Disconnect, stop third-party trackers altogether. It also shows you how many tracking companies are working in the background of the Web sites you visit. It still lets what are known as first-party trackers keep tabs on you. That means, Mr. Kennish said, that Amazon can still keep tabs on the kinds of books you buy to recommend others. But your book-browsing history is not monitored by other companies trying to target their ads. You will still see ads. They just won’t be based on your behavior on the Web.